The present invention relates to a device for spinal fixation, and in particular to a transconnector for coupling spinal rods, plates, or other elongate members.
It is often necessary to surgically treat spinal disorders such as scoliosis. Numerous systems for use in spinal correction and fixation have been disclosed. These systems usually include a pair of elongate members, typically either rods or plates, placed along the vertebral column. For the sake of simplicity, the term xe2x80x9crodxe2x80x9d is used throughout to refer to any elongate member. Each rod is attached to the spine with various attachment devices. These attachment devices may include, but are not limited to, pedicle screws, plates, transverse process hooks, sublaminar hooks, pedicle hooks, and other similar devices.
It is also well known that the strength and stability of the dual rod assembly can be increased by coupling the two rods with a cross-brace or transconnector which extends substantially horizontal to the longitudinal axes of the rods across the spine. The simplest situation in which a transconnector could be used occurs when the two rods are geometrically aligned. Specifically, the two rods are parallel to each other, i.e. there is no rod convergence or divergence in the medial-lateral direction; the two rods have the same orientation with respect to the coronal plane (viewed in the anterior-posterior direction), i.e. the rods are coplanar from a lateral view; and the two rods are located a uniform distance from each other.
Due to a wide variety of factors, the two rods are rarely three dimensionally geometrically aligned in clinical situations. There are several ways to address the variations of geometrical alignment. First, one or both of the rods can be bent to accommodate the transconnector. However, any bending in either of the rods can adversely affect the fixation to the spine and comprise clinical outcome. Furthermore, the bending can also adversely affect the mechanical properties of the rods. The transconnector can also be bent so that the disturbance to the rod positioning is minimized. As is the case with bending of the rods, the mechanical properties of the transconnector could be compromised.
Transconnectors with some adjustability have been designed to adapt for variations from geometrical alignment. However, most are multi-piece systems that can be difficult to assemble and use in the surgical environment. U.S. Pat. No. 5,980,523 discloses a multi-piece transverse connector for spinal rods that can accommodate converging or diverging rods. However, accidental disassembly of the connector by the surgeon is possible. Even those that are one-piece designs do not allow for adjustments to compensate for all three modes in which there may be variation from geometrical alignment: convergence or divergence, non-coplanar rods, and variability in rod separation distances. For example, U.S. Pat. No. 5,947,966 discloses a device for linking adjacent spinal rods. In one embodiment, the device includes two members that are movable with respect to one another to accommodate different rod separation distances. A pin on one member engages a groove on the other member to provisionally couple the two members, thereby preventing a surgeon from separating the two members. Because the pin is sized to exactly fit the groove, no movement of the pin transverse to the longitudinal axis of the groove is possible. As a result, the device disclosed in the ""966 patent cannot accommodate non-coplanar rods or adjust for rod convergence or divergence.
Thus, there exists a need for an improved transconnector for coupling spinal rods.
The present invention relates to a transconnector for coupling first and second elongate spinal fixation elements that have different three dimensional orientations. The transconnector includes a male member, a female member and a locking member and can be made of any suitable material such as titanium, a titanium alloy, or stainless steel. The male member comprises a body with lateral and medial ends, a linking element associated with the lateral end and being configured and dimensioned to receive one of the fixation elements, and a projection on the medial end. The projection includes a body with a recess defined by lateral and medial walls. The female member comprises a body with lateral and medial ends, a linking element associated with the lateral end and being configured and dimensioned to receive one of the fixation elements, and a cavity with an opening on the medial end which is configured and dimensioned to receive a portion of the male member projection. The locking member secures the position and orientation of the male member projection portion in the cavity in order to accommodate different separation distances and orientations between the first and second fixation elements. The locking member interacts with the medial wall of the recess to limit travel of the male member projection portion in the cavity, thereby preventing uncoupling of the male and female members.
Preferably, the locking member comprises a threaded hole in the body of the female member and a set screw threadably received in the threaded hole. The set screw has a first end for receiving a tool to turn the set screw and a second end contactable with the projection for pressing the projection against the cavity. The recess may have a width wider than a width of the second end of the set screw for the rotation of the projection in the cavity. In an exemplary embodiment, the projection has a substantially cylindrical shape with a first radius and the recess has a curved upper surface with a second radius. The first radius is larger than the second radius and the second end of the set screw extends into the recess to limit the rotation of the projection in the cavity. The set screw can be a threaded cylindrical body transitioning to a tip at the second end of the set screw.
The male member body may comprise a link terminal having a lateral end with the male member linking element, an intermediate link having a medial end with the projection of the male member and a lateral end engaging the medial end of the link terminal, and a locking element for securing the link terminal to the intermediate link. Preferably, the medial end of the link terminal includes a first textured surface and the lateral end of the intermediate link includes a second textured surface mating with the first textured surface. The first textured surface is rotatable with respect to the second textured surface for accommodating convergence or divergence between the first and second rods. An example of suitable first and second textured surfaces includes a radial or star-grind pattern.
The locking element preferably comprises a first hole through the medial end of the link terminal, a second hole through the lateral end of the intermediate link aligned with the first hole, and a cap screw insertable in the first and second holes. The cap screw may have a second end with a retaining ring for preventing removal of the cap screw from the second hole. The retaining ring may include a resilient member which flexes inward upon insertion of the cap screw through the second hole and flexes outward once the resilient member is past a collar in the second hole. Preferably, the resilient member includes an end of the cap screw with a lip and a plurality of slits.
If rods are used for the elongate fixation elements, then the male member linking element preferably comprises a hook and the female member linking element preferably comprises a hook. The lateral ends of the male and female members each may include a threaded hole and a clamping screw threadably received in the respective threaded hole for securing the fixation elements to the respective hook. The fixation elements are preferably clamped between a conical second body portion of the respective clamping screw and a region near the tip portion of the respective hook when the transconnector is secured to the fixation elements.